1. Technical Field
The present invention relates to a method of manufacturing ferroelectric memory devices.
2. Related Art
Ferroelectric memory devices (FeRAM), which are non-volatile memory devices capable of operating at high speeds but at low voltages, are expected to be the future large-capacity non-volatile memory. Their memory cells may be arrayed in the 1 transistor/1 capacitor (1T/1C) configuration, enabling large-capacity integration at the same level as that of DRAM.
To maximize the ferroelectric properties of the ferroelectric capacitors composing a ferroelectric memory device, the crystal orientations in the layers composing a ferroelectric capacitor are critical. Specifically, to control the crystal orientation of the ferroelectric film, crystal orientation and flatness must be controlled from a lower electrode film disposed on the underside of the ferroelectric film.
On the other hand, a stack structure, in which capacitors are formed on contact plugs connected to transistors, is known as a method for improving the integration level of the capacitors as disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-134692.
Regarding capacitors disposed in a stack structure, a ferroelectric film is formed on two different surfaces, namely those of an insulating film and a contact plug. Thereby, controlling the crystal orientations in these films is very important.
There is a problem in that the bottom of a recess, namely a depression, formed on the contact plug must be flat. A satisfactory level of the crystal orientation of the lower electrode formed on the contact plug can not be always be achieved by the conventional art disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-134692 mentioned above, which includes: covering the whole surface of the formed contact plug with a conductive hydrogen barrier film; flattening the whole surface covered with the conductive hydrogen film until the recess is filled using any technique such as CMP; and, forming a lower electrode is formed thereon.